Many solutions are available on the market for condensation heat exchangers providing the use of a coil.
Particularly, by Italian patent n° 1396729 (corresponding to EP application 2504632), the same Applicant has proposed a solution providing a condensation heat exchanger with two separated spiral wound tubes, respectively one plain (inner) and the other one corrugated (outer).
Pairing of these two different coils permits obtaining an optimum heat exchange, by differentiating the type of exchange surface as a function of the fluid temperature with which it meets. Within the combustion chamber, characterized by high temperatures caused by combined effects of heat exchange due to irradiation and convection, it is provided a heat exchanger comprised of a plain coil, while in zone with lower fume temperature, where condensation phenomenon of gaseous compound starts, it is provided a second corrugated coil, to maximize heat exchange ad promote proper outflow of condensate. Two coils are placed in series with respect to the gaseous products flow and in parallel with respect to the heat carrier fluid.
However, while developing the solution described in IT'729, it has been discovered that the solution suggested does not permit completely obtaining the results set, as far as heat exchanger costs, reliability of the same, corrosion resistance, mechanical resistance and efficiency are concerned.
Particularly, it has been determined that fume circuit described in IT'729 does not permit obtaining the maximum efficiency during condensation heat exchange with outer coil.
Further, it has been found that corrugated outer coil is not convenient as far as reliability against corrosion and mechanical resistance are concerned.
Furthermore, solution suggested in IT'729 does not permit optimizing efficiency since turns of first and/or second coil can prevent an optimum passage of fumes.